Apparatus for monitoring nox removal catalyst of denitrizer and method of monitoring nox removal catalyst

ABSTRACT

To provide an NO x  removal catalyst management unit for use with an NO x  removal apparatus, the management unit detecting an NO x  removal catalyst layer that is actually deteriorated, whereby the deteriorated catalyst layer can be effectively replaced by a new catalyst layer, and to provide a method for managing the NO x  removal catalyst.  
     The management unit for managing a plurality of NO x  removal catalyst layers provided in a flue gas NO x  removal apparatus includes NO x  measurement means  16 A through  16 E for determining NO x  concentrations on the inlet and outlet sides of respective NO x  removal catalyst layers  14 A through  14 D; NH 3  measurement means  17 A through  17 E for determining NH 3  concentrations on the inlet and outlet sides of the same NO x  removal catalyst layers; and percent NO x  removal determination means  18  for determining percent NO x  removal (η) on the basis of an inlet mole ratio (i.e., inlet NH 3 /inlet NO x ).

TECHNICAL FIELD

The present invention relates to an NO_(x) removal catalyst managementunit for use with an NO_(x) removal apparatus, the management unit beingprovided for carrying out performance management on an NO_(x) removalcatalyst included in a flue gas NO_(x) removal apparatus installed in afacility such as a thermal power station, and to a method for managingthe NO_(x) removal catalyst.

BACKGROUND ART

Conventionally, boilers provided in thermal power stations and a varietyof large-scale boilers employing a fuel such as petroleum, coal, or fuelgas, waste incinerators, and similar apparatuses have been equipped witha flue gas NO_(x) removal apparatus which contains a plurality of NO_(x)removal catalyst layers.

The above employed NO_(x) removal catalysts assume the form ofhoneycomb, plate, etc. During use, the catalytic performance of thecatalysts is problematically deteriorated with elapse of time as aresult of deposition, on the surface of the catalyst, of a substancewhich deteriorates the catalytic performance (hereinafter referred to asdeteriorating substance) or through migration of the dissolveddeteriorating substance into the catalyst.

Conventionally, the performance of the NO_(x) removal catalysts has beenmanaged by measuring NO_(x) concentration and unreacted NH₃concentration on the inlet and outlet sides of respective catalysts.When a drop in total performance of a catalyst system is confirmed, oldcatalysts are replaced with new catalysts or regenerated catalysts inorder of use age, and such replacement is carried out periodically.

Generally, NO_(x) removal catalysts are very expensive. Thus, there hasbeen proposed one approach for prolonging the service life of the NO_(x)removal catalysts to as long a duration as possible by assessing theperformance of each unit catalyst (Japanese Patent Publication (kokoku)No. 7-47108).

However, the aforementioned catalyst managing method has a drawback.According to the method, NO_(x) concentration and unreacted NH₃concentration of each catalyst layer are determined, and percent NO_(x)removal and percent contribution of each catalyst layer are calculatedfrom the determined NO_(x) concentration. On the basis of these values,performance-deteriorated catalysts are replaced with new catalysts inorder of degree of deterioration. In this case, when the catalyticperformance is evaluated by the percent contribution calculated on thebasis of the NO_(x) concentration, the catalyst layer(s) having actuallydeteriorated performance cannot be detected correctly.

In view of the foregoing, an object of the present invention is toprovide an NO_(x) removal catalyst management unit for use with anNO_(x) removal apparatus, the management unit detecting an NO_(x)removal catalyst layer that is actually deteriorated, whereby thedeteriorated NO_(x) removal catalyst layer can be effectively replacedby a new catalyst layer. Another object of the invention is to provide amethod for managing the NO_(x) removal catalyst.

DISCLOSURE OF THE INVENTION

In order to attain the aforementioned objects, a first mode of thepresent invention provides an NO_(x) removal catalyst management unitfor use with an NO_(x) removal apparatus, the management unit beingprovided for managing a plurality of NO_(x) removal catalyst layersprovided in a flue gas NO_(x) removal apparatus, characterized in thatthe management unit comprises NO_(x) measurement means for determiningNO_(x) concentrations on the inlet and outlet sides of respective NO_(x)removal catalyst layers; NH₃ measurement means for determining NH₃concentrations on the inlet and outlet sides of the same NO_(x) removalcatalyst layers; and percent NO_(x) removal determination means fordetermining percent NO_(x) removal (η) on the basis of an inlet moleratio (i.e., inlet NH₃/inlet NO_(x)).

According to the first mode, NO_(x) concentrations and NH₃concentrations are determined on the inlet and outlet sides ofrespective NO_(x) removal catalyst layers, and the percent NO_(x)removal (η) is determined on the basis of an inlet mole ratio.Therefore, the percent NO_(x) removal, which is enhanced as the moleratio increases, can be evaluated on an absolute basis and correctly.

A second mode of the present invention is drawn to a specific embodimentof the NO_(x) removal catalyst management unit of the first mode for usewith an NO_(x) removal apparatus, wherein the percent NO_(x) removal (η)is determined on the basis of NH₃ concentrations.

According to the second mode, the percent NO_(x) removal (η) of each andevery NO_(x) removal catalyst layer is determined on the basis of NH₃concentrations rather than on the basis of NO_(x) concentrations.Therefore, the catalytic performance can be detected with smallervariation.

A third mode of the present invention is drawn to a specific embodimentof the NO_(x) removal catalyst management unit of the second mode foruse with an NO_(x) removal apparatus, wherein the percent NO_(x) removal(η) is determined on the basis of the following equation (1):η={(inlet NH₃−outlet NH₃)/(inlet NH₃−outlet NH₃+outletNO_(x))}×100×(evaluation mole ratio/inlet mole ratio)  (1).

According to the third mode, the percent NO_(x) removal (η) ofrespective NO_(x) removal catalyst layers can be detected withoutvariation and correctly, thereby managing respective NO_(x) removalcatalysts successfully and effectively.

A fourth mode of the present invention is drawn to a specific embodimentof the NO_(x) removal catalyst management unit of any of the first tothird modes for use with an NO_(x) removal apparatus, which managementunit further includes transmission means for transmitting concentrationvalues determined by the NO_(x) measurement means and the NH₃measurement means to the percent NO_(x) removal determination means,wherein the percent NO_(x) removal determination means determines thepercent NO_(x) removal (η) of respective NO_(x) removal catalyst layersincluded in a plurality of flue gas NO_(x) removal apparatuses.

According to the fourth mode, NO_(x) removal catalysts included in aplurality of flue gas NO_(x) removal apparatuses can be collectivelymanaged, thereby effectively managing NO_(x) removal catalysts.

A fifth mode of the present invention provides a method for managing anNO_(x) removal catalyst for use with an NO_(x) removal apparatus, themethod being provided for managing a plurality of NO_(x) removalcatalyst layers provided in a flue gas NO_(x) removal apparatus,characterized in that the method comprises determining NO_(x)concentrations and NH₃ concentrations on the inlet and outlet sides ofrespective NO_(x) removal catalyst layers; determining percent NO_(x)removal (η) on the basis of an inlet mole ratio (i.e., inlet NH₃/inletNO_(x)); and evaluating performance of respective NO_(x) removalcatalyst layers on the basis of the percent NO_(x) removal (η).

According to the fifth mode, NO_(x) concentrations and NH₃concentrations are determined on the inlet and outlet sides ofrespective NO_(x) removal catalyst layers, and the percent NO_(x)removal (η) is determined on the basis of an inlet mole ratio.Therefore, the percent NO_(x) removal, which is enhanced as the moleratio increases, can be evaluated on an absolute basis and correctly.

A sixth mode of the present invention is drawn to a specific embodimentof the method for managing an NO_(x) removal catalyst of the fifth modefor use with an NO_(x) removal apparatus, wherein the percent NO_(x)removal (η) is determined on the basis of NH₃ concentrations.

According to the sixth mode, the percent NO_(x) removal (η) ofrespective NO_(x) removal catalyst layers is determined on the basis ofNH₃ concentrations rather than on the basis of NO_(x) concentrations.Therefore, the catalytic performance can be detected without variation.

A seventh mode of the present invention is drawn to a specificembodiment of the method for managing an NO_(x) removal catalyst of thesixth mode for use with an NO_(x) removal apparatus, wherein the percentNO_(x) removal (η) is determined on the basis of the following equation(1):η={(inlet NH₃−outlet NH₃)/(inlet NH₃−outlet NH₃+outletNO_(x))}×100×(evaluation mole ratio/inlet mole ratio)  (1).

According to the seventh mode, the percent NO_(x) removal of each NO_(x)removal catalyst layer can be detected without variation and correctly,thereby managing respective NO_(x) removal catalysts successfully andeffectively.

An eighth mode of the present invention is drawn to a specificembodiment of the method for managing an NO_(x) removal catalyst of anyof the fifth to seventh modes for use with an NO_(x) removal apparatus,wherein the method further comprises performing restoration treatment ofan NO_(x) removal catalyst layer having a catalytic performancedeteriorated to a predetermined level, on the basis of results ofperformance evaluation of the respective NO_(x) removal catalyst layers.

According to the eighth mode, the percent NO_(x) removal of each NO_(x)removal catalyst layer is determined without variation and correctly,and the performance restoration treatment is carried out on the basis ofthe results. Thus, respective NO_(x) removal catalysts can beeffectively used.

A ninth mode of the present invention is drawn to a specific embodimentof the method for managing an NO_(x) removal catalyst of the eighth modefor use with an NO_(x) removal apparatus, wherein the performancerestoration treatment is replacement of the NO_(x) removal catalystlayer with a new NO_(x) removal catalyst layer, replacement of theNO_(x) removal catalyst layer with a regenerated NO_(x) removal catalystlayer, replacement of the NO_(x) removal catalyst layer with an NO_(x)removal catalyst layer inverted with respect to the direction of theflow of discharge gas, or replacement of the NO_(x) removal catalystlayer with an NO_(x) removal catalyst layer from which a deterioratedportion has been removed.

According to the ninth mode, the performance of deteriorated NO_(x)removal catalysts can be restored through any of the above treatments.

A tenth mode of the present invention is drawn to a specific embodimentof the method for managing an NO_(x) removal catalyst of any of thefifth to ninth modes for use with an NO_(x) removal apparatus, whereinthe method further comprises determining the percent NO_(x) removal ofrespective NO_(x) removal catalyst layers included in a plurality offlue gas NO_(x) removal apparatuses and evaluating catalytic performanceof respective NO_(x) removal catalyst layers included in a plurality offlue gas NO_(x) removal apparatuses.

According to the tenth mode, NO_(x) removal catalysts included in aplurality of flue gas NO_(x) removal apparatuses can be collectivelymanaged, thereby effectively managing NO_(x) removal catalysts.

As described hereinabove, the present invention employs an NO_(x)removal catalyst management unit for use with an NO_(x) removalapparatus, which management unit comprises NO_(x) measurement means fordetermining NO_(x) concentrations on the inlet and outlet sides ofrespective NO_(x) removal catalyst layers; NH₃ measurement means fordetermining NH₃ concentrations on the inlet and outlet sides of the sameNO_(x) removal catalyst layers; and percent NO_(x) removal determinationmeans for determining percent NO_(x) removal (η) on the basis of aninlet mole ratio (i.e., inlet NH₃/inlet NO_(x)). Therefore, themanagement unit detects an NO_(x) removal catalyst layer that isactually deteriorated, whereby the deteriorated catalyst layer can beeffectively replaced by a new catalyst layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a configuration of a flue gas NO_(x) removalapparatus equipped with an NO_(x) removal catalyst management unitaccording to an embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 schematically shows a configuration of a flue gas NO_(x) removalapparatus equipped with an NO_(x) removal catalyst management unitaccording to an embodiment of the present invention. Actually, the fluegas NO_(x) removal apparatus is provided in a thermal power station.However, no particular limitation is imposed on the facility thatincludes the NO_(x) removal catalyst management unit of the embodiment.

As shown in FIG. 1, a flue gas NO_(x) removal apparatus 10 includes anexhaust duct 12 and a treated gas duct 13. The exhaust duct 12 is incommunication with a boiler unit installed in a thermal power stationthat is connected with an apparatus body 11 on the upstream side. Thetreated gas duct 13 is connected with the apparatus body 11 on thedownstream side. In the apparatus body 11, a plurality of NO_(x) removalcatalyst layers (4 layers in this embodiment) 14A to 14D are disposed atpredetermined intervals. The NO_(x) removal catalyst layers 14A to 14Dare arranged so that a discharge gas introduced through the exhaust duct12 is sequentially passed therethrough, and reduce the level of nitrogenoxide (NO_(x)) of the discharge gas through contact with the dischargegas passing through the catalyst layers. Notably, to the exhaust duct 12communicating with the boiler unit, NH₃ is injected in an amount inaccordance with the amount of the discharge gas fed from the boilerbody.

No particular limitation is imposed on the type, shape, etc. of thecatalysts 14A to 14D. Generally, each catalyst is composed of TiO₂serving as a carrier and V₂O₅ serving as an active component. Thecatalysts assume the form of honeycomb, plate, etc.

In the present embodiment, each catalyst layer employs a catalyst in theform of columnar honeycomb, and a plurality of catalyst layers arearranged in combination, thereby forming the catalyst layers 14A to 14D.

An NO_(x) removal catalyst management unit 20 of the present embodimentis provided with gas sampling means 15A through 15E on the inlet andoutlet sides of respective NO_(x) removal catalyst layers 14A through14D. The gas sampling means 15A through 15E are connected with NO_(x)concentration measurement means 16A through 16E and with NH₃concentration measurement means 17A through 17E. The data obtained bythe measurement means are transferred to a percent NO_(x) removaldetermination means 18 for calculating percent NO_(x) removal andpercent NO_(x) removal contribution of the respective NO_(x) removalcatalyst layers 14A through 14D.

The gas sampling means 15A through 15E sample, via sampling tubes, a gasto be sampled in a desired amount and at a desired timing, andsubsequently feed the sampled gas to the NO_(x) concentrationmeasurement means 16A through 16E and to the NH₃ concentrationmeasurement means 17A through 17E. Notably, the sampling tubes andsimilar parts which are in contact with a gas to be sampled are requiredto be made of a material which has a predetermined heat resistance andwhich is inert to the corresponding gas. In the present embodiment, thegas sampling means 15A through 15E feed the sampled gas to the NO_(x)concentration measurement means 16A through 16E and to the NH₃concentration measurement means 17A through 17E. However, needless tosay, each of the NO_(x) concentration measurement means 16A through 16Eand the NH₃ concentration measurement means 17A through 17E may beprovided with gas sampling means.

No particular limitation is imposed on the timing for sampling a gas bythe gas sampling means 15A through 15E. Generally, sampling is carriedout during usual operation of the power station, preferably at thenominal load where the amount of gas reaches the maximum, if possible.The interval between sampling operations may be prolonged to about sixmonths, and the interval is sufficient for managing the performance ofthe NO_(x) removal catalyst layers 14A through 14D. However, if theinterval is shortened, precision in management is enhanced. Thus, thesampling is preferably carried out, for example, once every one to twomonths. Particularly, in a catalyst layer placed on the downstream side,variation of obtained data increases due to decrease in NH₃concentration. Thus, in order to attain better management andevaluation, preferably, determination of NH₃ concentration is performedat short intervals, and percent NO_(x) removal is calculated from anaveraged NH₃ concentration value.

No particular limitation is imposed on the NO_(x) concentrationmeasurement means 16A through 16E and the NH₃ concentration measurementmeans 17A through 17E, so long as the measurement means can determinethe NO_(x) concentration measurement and the NH₃ concentration of thesample gas. Although an automated measuring apparatus is preferred,manual analysis means may also be employed. Needless to say, the NO_(x)concentration and the NH₃ concentration may be directly determined bymeans of a sensor without sampling the gas.

As described above, the NO_(x) concentration and the NH₃ concentrationof the sampled gas are determined. In addition, oxygen or othercomponents may also be determined, if required.

According to the present embodiment, NO_(x) measurement means and NH₃measurement means are provided on the inlet and outlet sides ofrespective NO_(x) removal catalyst layers 14A through 14D.Alternatively, a single NO_(x) concentration measurement means and asingle NH₃ concentration measurement means are provided, and NO_(x)concentrations and NH₃ concentrations on the inlet and outlet sides ofrespective NO_(x) removal catalyst layers 14A through 14D may beanalyzed sequentially. In this case, sampling of gas may be performedsequentially in accordance with measurement. Although time lags occurduring sampling, they would not be any problem so long as the NO_(x)removal operation proceeds consistently. However, it is preferred thatsampling be simultaneously performed and the sampled gases besequentially fed to the corresponding measurement means for analysis.

The percent NO_(x) removal determination means 18 collects themeasurement data from the NO_(x) concentration measurement means 16Athrough 16E and the NH₃ concentration measurement means 17A through 17E,and calculates, from the measurement data, percent NO_(x) removal andpercent NO_(x) removal contribution of respective NO_(x) removalcatalyst layers 14A through 14D. No particular limitation is imposed onthe method of calculating percent NO_(x) removal, and any method may beemployed so long as the percent NO_(x) removal is calculated on thebasis of an inlet mole ratio (i.e., inlet NH₃/inlet NO_(x)) of theNO_(x) removal catalyst layers 14A through 14D.

The reason for taking the inlet mole ratio into consideration is asfollows. NH₃ is fed into an NO_(x) removal apparatus in the vicinity ofNO_(x) removal catalysts on the upstream side in an amount proportionalto that of the gas to be treated. The rate determining step of NO_(x)removal reaction is a step of adsorbing NH₃ onto the catalysts.Therefore, it is most critical to detect NH₃ concentrations on the inletand outlet sides of the NO_(x) removal catalyst layers 14A through 14Dupon management of the performance of the NO_(x) removal catalyst layers14A through 14D on the basis of NH₃ concentrations.

When calculated on the basis of an inlet mole ratio, the percent NO_(x)removal may be calculated from NO_(x) concentration or NH₃concentration. However, NH₃-basis calculation provides percent NO_(x)removal values of higher precision suitable for management.

An exemplary procedure of deriving percent NO_(x) removal will next bedescribed. The percent NO_(x) removal (η) is determined on the basis ofthe following equation (2) employing NO_(x) concentrations:η={(inlet NO_(x)−outlet NO_(x))/(inlet NO_(x))}×100×(evaluation moleratio/inlet mole ratio)  (2).

As used herein, the term “evaluation mole ratio” refers to a mole ratiowhich is predetermined for the purpose of evaluating an NO_(x) removalcatalyst. The evaluation mole ratio may be predetermined to an arbitraryvalue; for example, 0.8, which is almost equal to a mole ratio typicallyemployed for operating a power station.

Although the percent NO_(x) removal (η) is determined on the basis ofthe equation employing NO_(x) concentrations, target catalysts can beevaluated on the basis of a percent NO_(x) removal value actuallyreflecting the conditions of a catalyst, since the equation employs aninlet mole ratio. In general, since the percent NO_(x) removal increaseswith NH₃/NO_(x), the percent NO_(x) removal must be derived on the basisof the inlet mole ratio so as to evaluate catalysts in an actual state.

The percent NO_(x) removal (η) is also determined on the basis of thefollowing equation (1) employing NH₃ concentrations:η={(inlet NH₃−outlet NH₃)/(inlet NH₃−outlet NH₃+outletNO_(x))}×100×(evaluation mole ratio/inlet mole ratio)  (1).

Since the percent NO_(x) removal (η) is determined on the basis of theequation employing NH₃ concentrations, variation in the obtained percentNO_(x) removal values is smaller as compared with the case in which theequation employing NO_(x) concentrations is used, which is advantageous.Thus, catalysts can be evaluated on the basis of percent removal valueswith smaller variation.

According to the present invention, percent NO_(x) removal (η) ofrespective NO_(x) removal catalyst layers 14A through 14D is determinedthrough a technique on the basis of the inlet mole ratio, and theperformance of the catalysts is managed on the basis of the determinedpercent NO_(x) removal values. Specifically, when the percent NO_(x)removal of a certain catalyst drops below a predetermined level, thecatalyst having deteriorated performance undergoes performancerestoration treatment. According to the invention, a catalyst which hasbeen most deteriorated or a catalyst having a lowered percent NO_(x)removal value below a predetermined level is exclusively subjected toperformance restoration treatment. Therefore, NO_(x) removal catalystscan be effectively used without performing unnecessary restorationtreatment.

As used herein, the term “performance restoration treatment” generallyrefers to replacement of deteriorated catalysts with new catalysts,replacement of deteriorated catalysts with catalysts which have beenregenerated by washing, or replacement of deteriorated catalysts withcatalysts which have undergone regeneration treatment. Particularly whena honeycomb catalyst is used, a regenerated or un-regenerated NO_(x)removal catalyst is placed such that the catalyst is inverted withrespect to the direction of the flow of discharge gas, or a deterioratedNO_(x) removal is replaced with a new NO_(x) removal catalyst from whicha deteriorated portion has been removed, whereby performance of thecatalyst is restored. Notably, such restoration treatments are conceivedon the basis of the finding of the present applicant that the upstreamside of the discharge gas flow exclusively plays a great role in NO_(x)removal reaction.

In the aforementioned embodiment, NO_(x) removal catalysts of one fluegas NO_(x) removal apparatus are managed by means of a single NO_(x)removal catalyst management unit. Alternatively, NO_(x) removalcatalysts of a plurality of flue gas NO_(x) removal apparatuses may alsobe managed by means of a single NO_(x) removal catalyst management unit.Specifically, the percent NO_(x) removal data obtained by the percentNO_(x) removal determination means 18 may be transmitted in a wired orwireless manner to a central control system, whereby the percent NO_(x)removal data are collectively controlled. Alternatively, concentrationdata obtained by NO_(x) concentration measurement means 16A to 16E andNH₃ concentration measurement date 17A to 17E may be transmitted to acentral control system, whereby the percent NO_(x) removal data arecollectively controlled. In any case, total performance evaluation ofcatalysts can be performed through collective management of a pluralityof flue gas NO_(x) removal apparatuses, thereby reliably attaining totalmanagement and effective performance management of NO_(x) removalcatalysts.

WORKING EXAMPLE

Table 1 shows the results of NO_(x) concentration measurement and NH₃concentration measurement on the inlet and outlet sides of fourrespective NO_(x) removal catalyst layers (similar to FIG. 1) of a fluegas NO_(x) removal apparatus installed in an actual thermal powerstation. The measurement was carried out seven times: 1st (starting),2nd (about 2 months after starting), 3rd (about 5 months afterstarting), 4th (about 7 months after starting), 5th (about 12 monthsafter starting), 6th (about 24 months after starting), and 7th (about 30months after starting).

As mentioned above, percent NO_(x) removal on the basis of NO_(x)concentration of each catalyst layer was calculated from measured NO_(x)concentrations and NH₃ concentrations, and the results are shown inTable 2. Percent NO_(x) removal on the basis of NH₃ concentrations ofeach catalyst layer was calculated in a similar manner, and the resultsare shown in Table 3.

Measurement was also performed with respect to the case where a portionof the second NO_(x) removal catalyst layer had been replaced with aregenerated catalyst (regenerated by washing with water; havingcatalytic performance equivalent to that of an unused product, confirmedby a performance test). In a similar manner, NO_(x) concentration andNH₃ concentration were measured on the inlet and outlet sides of thereplaced portion of the second catalyst layer. The results are alsoshown in Table 1. In addition, percent NO_(x) removal on the basis ofNO_(x) concentration of each catalyst layer was calculated from measuredNO_(x) concentrations and NH₃ concentrations, and percent NO_(x) removalon the basis of NH₃ concentrations of each catalyst layer was calculatedin a similar manner. The results are shown in Tables 2 and 3,respectively.

COMPARATIVE EXAMPLE

Percent NO_(x) removal and percent NO_(x) removal contribution of eachcatalyst layer were calculated on the basis of the following equation(3):η={(inlet NO_(x)−outlet NO_(x))/(inlet NO_(x))}×100  (3),

from NO_(x) concentrations measured on the inlet and outlet sides of thecatalyst layer in the Working Example. Table 4 shows the results. Thistechnique is based on the method disclosed in Japanese PatentPublication (kokoku) No. 7-47108. TABLE 1 2nd 3rd 4th 5th 12 6th 24 7th30 1st 2 months 5 months 7 months months months months Measurementstarting after after after after after after NO_(x) 1st layer 148.7166.6 208.3 228.1 221.6 166.7 175.9 concentration inlet (ppm) 2nd layer65 72.3 85.7 111.4 94.4 78.8 78.9 inlet 3rd layer 44.6 46.4 44.7 51.848.6 47.6 44.0 inlet 4th layer 42.4 44.9 41.1 48.8 45.6 45.4 40.2 inlet4th layer 39.4 39.4 36.9 44.2 43.3 42.3 38.0 outlet Ammonia 1st layer106.3 110.4 151.2 146.8 147.0 117.3 139.1 concentration inlet NH₃ (ppm)2nd layer 23.9 25.9 31.8 36.2 46.1 28.9 37.0 inlet 3rd layer 3 4 2.8 2.96.9 4.0 5.0 inlet 4th layer 3.2 2.2 2.3 1.8 5.4 3.0 2.0 inlet 4th layer0.7 1.8 0.7 0.5 1.7 0.5 0.8 outlet Regenerated 2nd layer 66.2 72.1 75.992.8 85.9 81.3 75.2 layer (2nd inlet layer) NO_(x) 2nd layer 46.4 47.750.3 58.0 55.2 56.9 46.8 concentration outlet Ammonia 2nd layer 24.127.8 29.5 36.4 39.9 28.4 41.9 concentration inlet NH₃ (ppm) 2nd layer6.8 9.2 9.1 11.2 16.1 10.4 10.5 outlet

TABLE 2 2nd 3rd 4th 5th 12 6th 24 7th 30 1st 2 months 5 months 7 monthsmonths months months Measurement starting after after after after afterafter Reduced to 1st layer 63.0% 68.3% 64.9% 63.6% 69.2% 59.9% 55.8%mole ratio 2nd layer 68.3% 80.0% 103.3% 131.8% 79.6% 86.5% 75.5% 0.8 3rdlayer 58.7% 30.0% 101.6% 81.5% 34.9% 42.7% 60.2% NO_(x) 4th layer 75.0%200.0% 147.6% 201.2% 33.1% 82.7% 90.9% Regenerated NO_(x) 65.7% 70.4%69.3% 76.5% 61.5% 68.9% 54.3% layer (2nd layer)

TABLE 3 2nd 3rd 4th 5th 12 6th 24 7th 30 1st 2 months 5 months 7 monthsmonths months months Measurement starting after after after after afterafter Reduced to 1st layer 62.6% 65.1% 64.2% 61.9% 62.3% 60.1% 57.1%mole ratio 2nd layer 69.4% 71.6% 84.9% 96.3% 73.2% 75.1% 71.8% 0.8 3rdlayer −5.6% 35.8% 15.7% 31.9% 18.1% 19.6% 49.7% NH₃ 4th layer 63.2%16.4% 60.9% 63.6% 53.6% 66.5% 48.1% Regenerated NH₃ 59.6% 58.2% 59.4%61.8% 51.9% 55.1% 57.7% layer (2nd layer)

TABLE 4 2nd 3rd 4th 5th 12 6th 24 7th 30 1st 2 months 5 months 7 monthsmonths months months Measurement starting after after after after afterafter Total percent NO_(x) 73.5% 76.4% 82.3% 80.6% 80.4% 74.6% 78.4%removal Percent 1st layer 76.6% 74.1% 71.5% 63.4% 71.3% 70.7% 70.3%contribution 2nd layer 18.7% 20.4% 23.9% 32.4% 25.7% 25.1% 25.3% 3rdlayer 2.0% 1.2% 2.1% 1.6% 1.7% 1.7% 2.7% 4th layer 2.7% 4.3% 2.5% 2.5%1.2% 2.5% 1.6% Total 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%<Performance Evaluation>

As is clear from Tables 1 to 4, percent NO_(x) removal values of thethird layer and the fourth layer calculated on the basis of only NO_(x)concentrations (Comparative Example) are very small from the firstmeasurement. The Test Example mentioned below has revealed that thesesmall values do not reflect the actual states of the catalyst layers.

In contrast, according to the method of the Working Example employingmole ratios (NH₃/NO_(x)) (inlet mole ratio and evaluation mole ratio),percent NO_(x) removal values on the basis of NH₃ concentrations andthose on the basis of NO_(x) concentrations were found to assess theactual states of the catalyst layers.

Through statistical processing of the data shown in Tables 2 and 3 ofthe Working Example so as to determine variation in a specific data set,percent NO_(x) removal values calculated on the basis of NH₃concentrations were found to have less variation. This was confirmedthrough the following procedure.

In the Working Example, since the evaluation mole ratio was set to 0.8,the theoretical percent NO_(x) removal was 0 to 80% on the basis of theevaluation mole ratio. The incident of the values falling outside theabove range was counted in Tables 2 and 3. Table 5 shows the results.

A simple average was calculated for percent NO_(x) removal valuesobtained from the first measurement to seventh measurement shown inTables 2 and 3, and the incident of the simple average values exceedingthe theoretical percent NO_(x) removal was counted. The results areshown in Table 6.

From the data in Tables 2 and 3, unbiased variance in percent NO_(x)removal of each catalyst layer was calculated, and the obtained variancevalues were averaged. The percent NO_(x) removal values falling outsidethe theoretical range were removed from the data shown in Tables 2 and3, and approximate equations were derived from the remaining datathrough the least squares method. Pearson's product-moment correlationcoefficients of the equations (r), r² (RSQ), and averaged values thereofwere calculated. Table 7 shows the results. TABLE 5 Outside thetheoretical range Catalyst layers NH₃ NO_(x) 1st layer 0 0 2nd layer 2 33rd layer 1 2 4th layer 0 5 2nd layer 0 0 (regenerated) Total 3 10

TABLE 6 Average Catalyst layers NH₃ NO_(x) 1st layer 61.9%  63.5% 2ndlayer 77.5%  89.3% 3rd layer 23.6%  58.5% 4th layer 53.2% 118.6% 2ndlayer 57.7%  66.7% (regenerated) Outside the 0 2 theoretical range

TABLE 7 r² (RSQ)/least Catalyst Variance squares method layers NH₃NO_(x) NH₃ NO_(x) 1st layer 0.0007 0.0022 0.812 0.537 2nd layer 0.00940.0470 0.034 0.028 3rd layer 0.0310 0.0668 0.302 0.027 4th layer 0.03040.4260 0.031 0.168 2nd layer 0.0011 0.0050 0.167 0.351 (regenerated)Average 0.0145 0.1094 0.269 0.222

As is clear from Table 5, the incident of values falling outside thetheoretical percent NO_(x) removal range is larger in NO_(x) than inNH₃.

As is clear from Table 6, the incident of simple average values fallingoutside the theoretical percent NO_(x) removal range is larger in NO_(x)than in NH₃.

As is clear from Table 7, variance in NO_(x)-based percent NO_(x)removal values is larger than variance in NH₃-based percent NO_(x)removal values. From Table 7, the averaged RSQ in relation to the leastsquares method is greater in the case of NH₃ than in the case of NO_(x),indicating that NH₃-based percent NO_(x) removal values have highcorrelation. In the cases of the fourth layer and the regenerated secondlayer, RSQ values are lower in the case of NH₃ than in the case ofNO_(x). However, these values were obtained at unsatisfactorymeasurement precision, and the averaged correlation value is higher inthe case of NH₃. Therefore, NH₃-basis data are concluded to have lessvariance.

As is clear from Tables 5 to 7, time-dependent change in percent NO_(x)removal of each NO_(x) removal catalyst layer is smaller in the case ofNH₃-concentration-basis percent NO_(x) removal values than in the caseof NO_(x)-concentration-basis percent NO_(x) removal values.

From the NH₃-concentration-basis percent NO_(x) removal values shown inTable 3, the percent NO_(x) removal values falling outside thetheoretical range were removed, and approximate equations were derivedfrom the data falling within the theoretical range through the leastsquares method. On the basis of these approximate equations, percentNO_(x) removal of each catalyst layer (12 months after the start ofmeasurement) was calculated. Table 8 shows the results. TABLE 8 Catalystlayers 5th (after 12 months) 1st layer 62% 2nd layer 74% 3rd layer 28%4th layer 60% 2nd layer (regenerated) 58%

As is clear from Table 8, the most deteriorated NO_(x) removal catalystlayer is estimated to be the third layer. At the fifth point in time ofmeasurement, the degree of deterioration has been found to be in thesequence of the third layer, the regenerated second layer, the fourthand the first layers (approximately equal to each other), and the secondlayer.

In contrast, the results of the Comparative Example appear to indicatethat the percent contribution of the first layer decreased and that ofthe second layer increased, thereby maintaining the performance of theNO_(x) removal apparatus. That is, the first layer is concluded to bedeteriorated.

TEST EXAMPLE

A portion of each of the catalyst layers employed in the Working Examplewas sampled, and the sample was evaluated in performance through thefollowing method.

A portion (50 mm×50 mm×100 mm in length) was cut from the inlet side ofthe each NO_(x) removal catalyst layer, and set in a performance testmachine. The test gas was fed under the conditions which match thedesign values of an actual NO_(x) removal apparatus, and percent NO_(x)removal was determined by measuring NO_(x) concentration and NH₃concentration on the outlet side of the catalyst sample. The results areshown in Table 9.

The results indicate a certain degree of deterioration of catalystlayers, and are almost identical to the aforementioned deteriorationevaluation results.

As is clear from the above results, performance evaluation of NO_(x)removal catalysts carried out in the Working Example reflects actualdeterioration status; however, performance evaluation carried out in theComparative Example does not coincide with actual performanceevaluation. TABLE 9 Catalyst 1st 2nd 3rd 4th 2nd layer layers layerlayer layer layer (regenerated) Percent NO_(x) 78.5% 80.2% 69.1% 79.4%77.7% removal Order of 3 5 1 4 2 deterioration

1. An NO_(x) removal catalyst management unit for use with an NO_(x)removal apparatus, the management unit being provided for managing aplurality of NO_(x) removal catalyst layers provided in a flue gasNO_(x) removal apparatus, characterized in that the management unitcomprises NO_(x) measurement means for determining NO_(x) concentrationson the inlet and outlet sides of respective NO_(x) removal catalystlayers; NH₃ measurement means for determining NH₃ concentrations on theinlet and outlet sides of the same NO_(x) removal catalyst layers; andpercent NO_(x) removal determination means for determining percentNO_(x) removal (η) on the basis of an inlet mole ratio (i.e., inletNH₃/inlet NO_(x)), the inlet mole ratio being derived from an NO_(x)concentration which is an NO_(x) concentration as measured on the inletside by means of said NO_(x) measurement means and an NH₃ concentrationwhich is an NH₃ concentration as measured on the inlet side by means ofsaid NH₃ measurement means.
 2. An NO_(x) removal catalyst managementunit according to claim 1 for use with an NO_(x) removal apparatus,wherein the percent NO_(x) removal (η) is determined on the basis of NH₃concentrations.
 3. An NO_(x) removal catalyst management unit accordingto claim 2 for use with an NO_(x) removal apparatus, wherein the percentNO_(x) removal (η) is determined on the basis of the following equation(1):η={(inlet NH₃−outlet NH₃)/(inlet NH₃−outlet NH₃+outletNO_(x))}×100×(evaluation mole ratio/inlet mole ratio)  (1).
 4. An NO_(x)removal catalyst management unit according to any of claims 1 to 3 foruse with an NO_(x) removal apparatus, which management unit furtherincludes transmission means for transmitting concentration valuesdetermined by the NO_(x) measurement means and the NH₃ measurement meansto the percent NO_(x) removal determination means, wherein the percentNO_(x) removal determination means determines the percent NO_(x) removal(η) of respective NO_(x) removal catalyst layers included in a pluralityof flue gas NO_(x) removal apparatuses.
 5. A method for managing anNO_(x) removal catalyst for use with an NO_(x) removal apparatus, themethod being provided for managing a plurality of NO_(x) removalcatalyst layers provided in a flue gas NO_(x) removal apparatus,characterized in that the method comprises determining NO_(x)concentrations and NH₃ concentrations on the inlet and outlet sides ofrespective NO_(x) removal catalyst layers; determining percent NO_(x)removal (η) on the basis of an inlet mole ratio (i.e., inlet NH₃/inletNO_(x)); and evaluating performance of respective NO_(x) removalcatalyst layers on the basis of the percent NO_(x) removal (η), theinlet mole ratio being derived from an NO_(x) concentration which is anNO_(x) concentration as measured on the inlet side and an NH₃concentration which is an NH₃ concentration as measured on the inletside.
 6. A method according to claim 5 for managing an NO_(x) removalcatalyst for use with an NO_(x) removal apparatus, wherein the percentNO_(x) removal (η) is determined on the basis of NH₃ concentrations. 7.A method according to claim 6 for managing an NO_(x) removal catalystfor use with an NO_(x) removal apparatus, wherein the percent NO_(x)removal (η) is determined on the basis of the following equation (1):η={(inlet NH₃−outlet NH₃)/(inlet NH₃−outlet NH₃+outletNO_(x))}×100×(evaluation mole ratio/inlet mole ratio)  (1).
 8. A methodaccording to any of claims 5 to 7 for managing an NO_(x) removalcatalyst for use with an NO_(x) removal apparatus, wherein the methodfurther comprises performing restoration treatment of an NO_(x) removalcatalyst layer having a catalytic performance deteriorated to apredetermined level, on the basis of results of performance evaluationof the respective NO_(x) removal catalyst layers.
 9. A method accordingto claim 8 for managing an NO_(x) removal catalyst for use with anNO_(x) removal apparatus, wherein the performance restoration treatmentis replacement of the NO_(x) removal catalyst layer with a new NO_(x)removal catalyst layer, replacement of the NO_(x) removal catalyst layerwith a regenerated NO_(x) removal catalyst layer, replacement of theNO_(x) removal catalyst layer with an NO_(x) removal catalyst layerinverted with respect to the direction of the flow of discharge gas, orreplacement of the NO_(x) removal catalyst layer with an NO_(x) removalcatalyst layer from which a deteriorated portion has been removed.
 10. Amethod according to any of claims 5 to 7 for managing an NO_(x) removalcatalyst for use with an NO_(x) removal apparatus, wherein the methodfurther comprises determining the percent NO_(x) removal of respectiveNO_(x) removal catalyst layers included in a plurality of flue gasNO_(x) removal apparatuses and evaluating catalytic performance ofrespective NO_(x) removal catalyst layers included in a plurality offlue gas NO_(x) removal apparatuses.
 11. A method according to claim 8for managing an NO_(x) removal catalyst for use with an NO_(x) removalapparatus, wherein the method further comprises determining the percentNO_(x) removal of respective NO_(x) removal catalyst layers included ina plurality of flue gas NO_(x) removal apparatuses and evaluatingcatalytic performance of respective NO_(x) removal catalyst layersincluded in a plurality of flue gas NO_(x) removal apparatuses.
 12. Amethod according to claim 9 for managing an NO_(x) removal catalyst foruse with an NO_(x) removal apparatus, wherein the method furthercomprises determining the percent NO_(x) removal of respective NO_(x)removal catalyst layers included in a plurality of flue gas NO_(x)removal apparatuses and evaluating catalytic performance of respectiveNO_(x) removal catalyst layers included in a plurality of flue gasNO_(x) removal apparatuses.